This system is used in North Eastern Middlesex and Northern Essex County. This is a duplex system.As of December 17th, 2012 Valley CMed is using only the narrow banded frequencies and PL tones. Ch-4 is the hailing channel for CMED (except for NorthEast CMED (Lawrence) which uses Ch 42); and CMED will then assign a channel on which the EMS unit will speak with the hospital on. The channels listed without a description are those on which CMed assigns an EMS unit to talk on. These channels are picked by Cmed based on location of respective EMS unit.